Your 2021 Alpine has the Suburban IW60 RL on demand water heater.. The (RL) means recirculation Loop and this unit is only installed OEM .. the Suburban IW60 available over the counter at RV parts stores Does Not have the RL feature
The noise you are hearing is the recirculation pump turning on and off to maintain a set water temp you have have dialed into your system display..
You can also turn the RL pump OFF if desired ( I would ) and be aware this IW60RL unit is having issues in the filed with pump leaks,etc
Video link explaining the RL feature......
https://youtu.be/RkTWPQ2hUe0